The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
CN core network
CRNTI cell radio network temporary identifier
DL downlink
DRX discontinuous reception
eNB node B/base station in an E-UTRAN system
EPC evolved packet core (CN of an LTE network)
E-UTRAN evolved UTRAN (LTE)
HARQ hybrid automatic repeat request
HSPA high speed packet access
ID identifier
LTE long term evolution
MAC medium access control
ms milli-seconds
PCH paging channel
PDCCH physical downlink control channel
PDSCH physical downlink shared channel
PRACH primary RACH
QoS quality of service
RACH random access channel
RLC radio link control
RNTI radio network temporary identifier
RRC radio resource control
SI system information
SRS sounding reference signals
TA timing advance
UE user equipment
UL uplink
URA UTRAN registration area
UTRAN universal terrestrial radio access network
Various different wireless technologies specify procedures which are primarily directed toward managing power consumption in user devices which have a limited (galvanic) power supply. The LTE system utilizes a DRX period which allows the UE to depower certain hardware for certain (pre-defined) periods of time and receive possible DL and/or UL radio resource allocations on which DL and/or UL data is sent to the UE only in the time between those DRX periods where UE has not depowered its hardware. While in the conventional RRC connected mode and the UE is mobile and moving among cells of the network, typically the UE will be exchanging data fairly frequently but the volume of data is low (for example, data exchange of a few to a few hundred kilobytes every 5-30 seconds). For a typical network subscriber there is relatively higher activity in the morning prior to the subscriber beginning his/her commute (for example, email, web-surfing, voice calls) and thereafter the data activity is reduced during the commute even though some of those same host applications might remain active (for example, news/social network updates, keep alive or status reports, and push emails). Similar peaks and valleys of user activity are common for other times of the day and similarly it is common that various services remain open on the user device during the inactive periods in which there might be some automatic data transfer for application level updates.
Cellular networks provide different RRC states: LTE utilizes an RRC Connected state for data transmission and a RRC Idle state for inactive standby operations in the network. In RRC Idle, no data transmission or related signaling occurs between the UE and the network and so when there is some automated data transfer for application level updates as above, the UE is kept in or moved to the RRC Connected state. Transitioning from RRC Idle to RRC Connected requires signaling between the UE and the access network as well as between the UE and the Core Network. The purpose of such signaling is for authentication, security, and QoS authorization functions before the actual service data can be exchanged between the UE and the network.
The DRX in LTE is operative at certain times while the UE is in the RRC connected state, similar activity levels as in the RRC Idle state. That is, for LTE the UE's reception frequency can be the same in the RRC Connected mode as in the Idle mode for receiving UE paging. However, UE mobility (i.e. cell change) in the LTE RRC Connected mode is always handled by network-controlled handovers whereas in the LTE Idle mode the UE utilizes cell reselection, i.e. UE-controlled mobility.
Different wireless technologies utilize similar modes. For example, the UTRAN (HSPA) system has the additional RRC Connected states of CELL_PCH state and URA_PCH state. In those states the active data transmission is not possible but the RRC connection is maintained between the UE and the UTRAN, which reduces the signaling between the UE and the UTRAN and avoids the signaling between the UE and the CN completely as it relates to transitions from the RRC Idle to the RRC Connected states. The RRC connection is maintained between the UE and the serving RNC without having the UE context in the Node B, and state transitions are controlled by the serving RNC by using UE-dedicated RRC signaling. The UE's mobility in these states is handled by the UE-initiated cell reselection, where the UE location is updated in the serving RNC by cell and URA updates from the UE. The cell update is used in the CELL_PCH state and is performed at every cell reselection, while the URA update is used in the URA_PCH state and is performed at every UTRAN registration change.
During development of LTE Release 8, the target for the DRX in the RRC Connected mode was to design the DRX in such way that the UE power consumption would be at the same level as the LTE Idle mode. From the DRX cycle point of view this can be realized when a “long DRX cycle” and the “on duration” (the latter being the scheduled time in which the UE is awake and reading the PDCCH to see if it is scheduled) can have same value as used in the RRC idle mode, and the “inactivity timer” can be set to a very short value. An example long DRX setting in LTE could be: DRX cycle=640 ms; on duration=10 ms; inactivity timer=5 ms, which is quite comparable for the LTE Idle mode setting of DRX cycle=640 ms and on duration=5 ms. This kind of DRX setting would reduce the activity time to 1/64, (1.56%), for receiving the possible downlink data transmission to the UE. In theory the DRX enables the UE to remain in a power saving mode for most of the time.
In practice the power savings are much less pronounced, as the LTE RRC Connected mode is limited by several factors. First, the UE still needs to perform handover measurements for detecting and measuring any new neighboring cells. It is recognized that these are co-located in time with downlink data reception as much as possible in the UE reception scheduler, and the measurement requirements are affected by the configured DRX periods so as to not overly disrupt the DRX operation. Second, the UE needs to send measurement reports to the network when any of several reporting criteria is triggered. As the LTE uplink utilizes HARQ and the measurement reports are sent in the RLC Acknowledge mode, the transmission of any measurement report interrupts the DRX and the UE then moves to the constant reception mode until the inactivity timer enables DRX operation once again. Third, at every cell change there will be a normal network-controlled handover based on the E-UTRAN handover decision. And fourth, the UE must always maintain the timing advance by having uplink transmission access and reception of a new TA value. A typical network may update its TA with a MAC TA command quite often, for example once every 160 ms or so. The TA update requires the UE to interrupt its DRX cycle and move to the constant reception mode.
Considering the typical user experience in the morning commute as noted above and the generally small size of cellular cells in urban areas through which most commuters move, the automatic data updates in passively open application level programs tend to keep the UE from realizing the power savings potential which the DRX intended. Every time the user moves toward a different cell the DRX will be interrupted for neighbor measurement reports and cell changes and additionally there may be further DRX interruptions for any new TA within or among cells. It is common for urban commuters to transmit multiple cells.
The inventors consider that forcing the UE to the RRC Idle mode during the morning commute or other periods of relative inactive data exchange is an incomplete solution for two reasons. First, the UE would still need to wake from its DRX to take and send neighbor measurement reports for handover purposes. Second, the UE would still need to receive the automatic data updates noted by example above, meaning a high signaling load (particularly in the LTE CN) for transitioning from the RRC Idle state to the RRC Connected state and establishing an S1 interface connection whenever this automated data is to be sent to or from the UE. What is needed in the art is a way to more fully realize at the UE the power savings which the DRX concept was meant to enable but which in practice often does not.